The society of manufacturing engineers (SME) recently hosted a technical evening with major Australian steel supplier, Interlloy. the event focused on new developments in the heat treatment of steel and presented an excellent networking opportunity. CNC machining expert, James Abbott reports
Machining high tensile steel and discover a crack in the bar? Ouch! Did you finish machining and only then discover the fault? Worse still, did the product go into service and your customer let you know? Cost you money in rework?
It’s guaranteed that stock you’re using is not heat treated using the induction quench and temper process. This process, known as Superquench is a unique heat treatment process that eliminates cracking. The steel is heated by electromagnetic induction and quenched by spray jets in a single line, before being rolled onto cooling racks. That’s right, one end of the bar hasn’t even been started, whilst the other end is finished.
Heat treatment of steel
The heat treatment of steel has not always been an exact science. With traditional steel processing, red-hot bundles are lifted out of a furnace and quenched in a polymer solution.
Whilst the process achieves the desired result, it has its flaws. Hot air is blown over the bars, so the bars closer to the air intake heat faster than bars at the other end, which means uneven heating. And as for the quenching process, bars at the centre of the bundle are insulated and cool significantly slower than bars on the outside of the bundle, which means a high differential in the mechanical results.
The shock of quenching can cause bars to bend at random, and sometimes, crack. The latter is more likely to occur in smaller diameter material, down to Ø20mm, particularly in 4140 (pictured).
How does Superquench work?
With Superquench, each bar receives the exact same treatment, maintaining consistent mechanical results throughout the batch. At the end of the process, bars remain straight, and most importantly, crack free.
The process can be controlled within a tolerance of 30 Brinnel Hardness. Bars individually pass through heating coils, which gradually increase the temperature of the bar, changing its colour to red-hot! As the bar exits the heating coils, it passes through a quench phase with jets spraying onto the bar at a consistent rate.
Because the process relies on electromagnetic induction heating, the temperature of the bar can be measured, not the air around a bundle. This means the process can be more accurately controlled and consistency in results can be maintained.
According to Rowan Smithers, State Sales Manager at Interlloy, “Milltech Martin Bright have one of only a few Superquench process lines in the world, and we’re lucky enough to have one here in Australia.”
The bar is not subjected to mechanical stress during the Superquench process so there is no heat treatment stress, because there is no stress build up that needs to be stress relieved, in contrast to the furnace process.
What’s in it for you?
• Less rework.
• Reliable consistency in hardness.
• Focus on Just in Time and Lean thinking methodologies.
• Cost savings on inventory.
• Big cuts when machining without the risk of stress relief.
• Competitively priced.
Currently not all sizes of bar are available.
According to Tony Green, National Sales Manager at Interlloy: “Up to Ø180mm can currently be processed, but plans are to process up to Ø220mm. The line is impressive to watch when it goes through the heating coils. The process hardens, quenches and tempers high tensile bar, all in the same line. Bars come out finished”.
* James Abbott is Managing Director of Challenge Engineering and the 2013 Sydney Chapter Chairperson of the Society of Manufacturing Engineers (SME).
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